Maximum Value of a function

Hi,

I'm putting together a worksheet for beam loads and sizing. I can plot the bending moment of the applied loads on the beam however, I am having difficulty getting an automatic command to output the maximum bending moment from the function. I want to use the maximum bending moment value as a variable and input further along my worksheet.

Is there a reason why the maximise function does not work? Is there another method that I can use here?

I'm using Mathcad Prime 3.0 and have attached Mathcad and PDF copies of the file.